The present invention relates to an exhaust gas recirculation system for an internal combustion engine, and, more particularly, to an exhaust gas recirculation system having a multifunction valve.
An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment.
EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine.
Some internal combustion engines include turbochargers to increase engine performance, and are available in a variety of configurations. When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted by a poppet-type EGR valve directly from the exhaust manifold. The percentage of the total exhaust flow which is diverted for introduction into the intake manifold of an internal combustion engine is known as the EGR rate of the engine.
The reintroduction of exhaust gases will occur naturally when the exhaust manifold pressure is higher than the turbocharger boost pressure. In a low pressure system, the pressure difference simply pushes At the exhaust gas into the air intake before the turbocharger compressor. The disadvantage of this approach is the potential fouling of the turbocharger compressor and the air-to-air intercooler of the engine, if so equipped.
High pressure systems typically pump exhaust gas directly into the intake manifold of the engine. However, when such a turbocharged engine operates under lower speed and high torque conditions, the boost pressure is higher than the exhaust manifold pressure and recirculation of exhaust gasses is not possible. Earlier approaches to address this problem have included using devices such as back pressure valves, restrictive turbines, throttle valves and venturi inlet systems. Each can be used to improve the back pressure to boost pressure gradient to some degree, but each approach results in increased fuel consumption.
In controlling EGR, simple valves are sometimes used to direct the flow of exhaust gases for EGR, but such valves are not readily adaptable to accommodate sophisticated EGR system designs. Also, while multi-port valves, such as the valve disclosed in U.S. Pat. No. 3,083,693, have been used in relatively stable environments, commercially available versions of such valves are generally inadequate to handle the harsh environment or the control complexity of sophisticated EGR systems.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an internal combustion engine provides an intake manifold fluidly connected to a block to supply combustion air to each combustion cylinder. The intake manifold has an air intake port and a first EGR inlet port. A secondary exhaust manifold is fluidly coupled to at least one of the plurality of combustion cylinders. The secondary exhaust manifold has an exhaust outlet port. A multipurpose valve has a first valve inlet port, a waste gas outlet port and a first EGR outlet port, wherein the first valve inlet port is fluidly connected to the exhaust outlet port of the secondary exhaust manifold, the waste gas outlet port is in communication with the atmosphere, and the first EGR outlet port is fluidly coupled to the first EGR inlet port of the intake manifold.
In another aspect of the invention, a multifunction valve for adjusting EGR in an internal combustion engine provides a valve body having a plurality of cavities; a valve cap defining an exhaust gas pocket; and a rotor having a first surface, a second surface, a selection port and an air pocket defined by the first surface.
In another aspect of the invention, a method of operating a multifunction valve in an EGR system for an internal combustion engine which generates exhaust gases provides the steps of: operating the multifunction valve in a first position to supply exhaust gas from a second exhaust manifold to a first exhaust manifold; and operating the multifunction valve in a second position to supply a portion of the exhaust gas from the second exhaust manifold to the first exhaust manifold and to at least partially open a waste port to waste a portion of the exhaust gases.